1. Field of the Invention
The present invention relates to a display device including a dither processing circuit.
2. Description of the Related Art
Recently, plasma display panels (hereinbelow abbreviated as PDPS) in which a plurality of discharge cells having the function of pixels are arranged in matrix fashion to constitute a two-dimensional image display panel have attracted attention. In a PDP, discharge cells are respectively caused to discharge in response to pixel data of each pixel, under the control of a video (image) signal, thereby forming a display image on the screen by the emission of light which accompanies the discharge. As the method of driving such a PDP, the subfield method is known, in which drive is conducted with the display period of a single field divided into a plurality of subfields (subperiods). For example, the display period of a single field may be divided into N subfields (namely, subfields SF1, SF2, . . . , SF(N)), in the order of weighting. In each subfield, there are executed an addressing step in which the pixels are set to the illuminated pixel condition or the extinguished pixel condition in accordance with pixel data, and emission sustaining (maintenance) step, in which only those pixels which are in the above-mentioned illuminated pixel condition are made to emit light for a period corresponding to the weighting of this subfield. Consequently, a single field contains a mixture of subfields in which light emission from discharge cells is caused in the emission sustaining step and subfields in which no light emission from discharge cells is caused (or extinction of the discharge cells is retained). Thus, in a single field period, intermediate brightness is observed corresponding to the total time for which light emission is performed in the respective subfields.
In a display device using a PDP, picture quality may be improved by increasing the number of perceived gradations. The number of perceived gradations increases if the drive as described above is combined with dither processing.
In the dither processing, for example, four vertically and horizontally adjacent pixels are designated as a single group, and four dither coefficients (for example, 0, 1, 2, 3) having mutually different coefficient values are added to the pixel data corresponding to the respective pixels of this group. The apparent (pseudo) number of gradations can be increased by such dither processing when four pixels are treated as a single pixel.
However, if dither coefficients are added to the pixel data, picture quality could be impaired because the so-called “dither noise” i.e., spurious patterns having no relationship with the original pixel data, is perceived.